topic b6- inheritance, variation and evolution

• dna

  • double helix structure
  • make up genetic code
• genome

  entire set of genetic material in an organism
• sexual reproduction

  • two parents
  • produce gametes by meiosis
  • mixture of genetics, from each parent
• asexual reproduction

  • one parent
  • produce identical offspring via mitosis
  • genetically identical offspring, no variation
• meiosis

  • the cell duplicates its dna before cell division
  • these pairs of chromosomes line up in the centre of the cell
  • the chromosomes are pulled apart to either side
  • the cells then divide again
  • this leaves 4 genetically different gametes/ sex cells
• genetic diagrams

  • discover off spring genotype
  • can be used to determine phenotypes (physical features) in offspring
• male

  xy
• female

  xx
• genetic variation

  • differences in the genes and alleles between organisms (genotypes)
  • caused by mutations
  • can lead to disorders such as polydactyl or cystic fibrosis
• environmental variation

  • physical differences (phenotypes) caused by factors other than genes such as food or exercise
• variation is caused by

  • genetics
  • environment
• evolution

  all of today's species have evolved from simple life forms that first started to develop over three billion years ago
• speciation

  when a species evolves so much it becomes an entirely new species
• extinction

  • when a species is wiped out and no longer exists
  • this could be due to environmental changes, a new predator or diseases, or competition for food/ shelter
• darwins theory

  • natural selection
  • also known as 'survival of the fittest'
• natural selection

  • organisms within species have different features (caused by alleles)
  • certain features will be beneficial in an environment more than others
  • the organisms with these features will outlive the ones who don't, and so will pass on their genes
  • this will produce strong offspring
  • eventually all organisms within a generation will have this 'advantageous allele' (feature)
• three domain system

  • archaea
  • bacteria
  • eukaryota
• archaea

  primitive bacteria
• bacteria

  true bacteria
• eukaryota

  • broad range of organisms
  • includes fungi, plants, animals and protists
• classification

  • kingdom
  • phylum
  • class
  • order
  • family
  • genus
  • species
• classification

  • a way of identifying ancestors
• homozygous

  two of the same alleles
• heterozygous

  two different alleles
• dominant

  an allele that is always expressed
• recessive

  an allele that is only expressed if both alleles are recessive
• punnet squares

  show inheritance
• inherited disorders

  • polydactyl
  • cystic fibrosis
• cystic fibrosis

  • recessive
  • carriers unaffected
• polydactyl

  • dominant
  • one allele needed
• embryo screening

  • detects disorders
  • ethical issues
• selective breeding

  1. pick parents with desired traits
  2. breed them
  3. select best offspring and breed again
  4. repeat over generations
• risk of selective breeding

  inbreeding -> genetic defects
• genetic engineering

  transfers genes for desired traits
• examples of genetic engineering

  • bacteria produce insulin
  • gm crops -> higher yield, pest resistance
• concerns of genetic engineering

  health and environmental impact
• fossils

  show species evolution
• types of fossils

  • mineral replacement (bones -> stone)
  • costs and impressions (footprints)
  • preserved remains (ice, amber)
• fossils

  gaps due to decay or geological changes
• antibiotic-resistant bacteria

  • mutations -> resistance (e.g. MRSA)
  • causes- overuse and incomplete courses
  • prevention- use antibiotics only when needed